The Left has traditionally assumed that human nature is so malleable, so perfectible, that it can be shaped in almost any direction. By contrast, a Darwinian science of human nature supports traditionalist conservatives and classical liberals in their realist view of human imperfectibility, and in their commitment to ordered liberty as rooted in natural desires, cultural traditions, and prudential judgments. Arnhart's email address is larnhart1@niu.edu.

Tuesday, April 26, 2016

Human beings generally desire to live out a complete and healthy life. Like other animals, they pass through a life cycle from birth to maturity to death. Every human society is organized to manage the changing desires associated with this life cycle, which passes through distinctive stages such as infancy, juvenility, adolescence, adulthood, and old age. Children, adults, and the old have different desires, and to satisfy these desires they must fill different roles in society. Although human beings will risk their lives for a good cause, they generally agree that to be fully happy one must live out one's natural life span. To do this, they must strive to live healthy lives. Much of the daily routine of life in every human society is devoted to satisfying the physical desires for bodily survival by eating, sleeping, and finding shelter.

There are at least four fundamental ways of making a living--foraging, farming, herding, and trading. Foragers live by hunting and fishing for wild animals and gathering wild plants. Farmers live by cultivating domesticated plants and herding domesticated animals. The cultivation of plants ranges from horticulture (tending small gardens using simple hand tools) to agriculture (cultivating large fields with plows and draft animals). In some areas that are too dry for cultivation, people can become predominantly herders or pastoralists. Throughout human history, human beings have engaged in trading one thing for another; and some people have been specialists in trading. Over the past 500 years, beginning in parts of Europe (such as the Italian city-states, the Dutch Republic, and England), trading has intensified in commercial societies that have become urbanized and industrialized, and most people live by buying and selling goods and services in markets.

Political philosophers from Aristotle to Adam Smith have recognized that how people make their living shapes the character of their social order. Smith and other Scottish philosophers saw historical progress in the movement through the four fundamental ways of making a living, and they saw the emergence of modern commercial societies as bringing unprecedented growth in population, prosperity, and liberty, so that ever more people could satisfy not only their natural desire for a complete and healthy life but all their other natural desires.

Stephen Sanderson's Human Nature and the Evolution of Society is a survey of the evidence from evolutionary science that confirms the reality of those natural desires as constituting evolved human nature and of the evolutionary progress through the four ways of making a living.

As Sanderson indicates, the debates among anthropologists over how to characterize the life of human foragers have often been debates over political philosophy. I would suggest that these debates began with the dispute between Hobbes, Locke, Rousseau, and Marx over the state of nature, because foraging bands are assumed to show evidence of how the earliest human ancestors lived and thus as showing original human nature. Rousseau wanted to see that original condition as a state of perfect peace and equality. Similarly, Marx wanted to see it as a state of communism. The inequality of modern bourgeois or capitalist societies could then be considered a departure from that original condition. By contrast, Hobbes and Locke saw human beings in the state of nature as hunter-gatherers living in small families but inclined to violent conflicts.

It is generally agreed that among foragers, men are the hunters and women are the gatherers, so that there is a sexual division of labor. Women do not usually hunt, because women do most of the child care, which is more compatible with gathering than hunting, and because men have the physical and mental skills that make them better hunters.

The importance of male hunting in providing animal protein has led some anthropologists to speak of early human evolution as the story of "man the hunter," which was the title of an important collection of papers on foraging bands published in 1968 and edited by Richard Lee and Irven DeVore. Lee was a Marxist anthropologist who wanted to see foraging bands as completely egalitarian. He also argued that most of the diet of foragers came from the food gathered by women rather than that hunted by men. This allowed some feminist anthropologists to say that the story of human evolution was the story of "woman the gatherer," and that foragers should be identified as "gatherer-hunters."

In the 1970s, some anthropologists (such as Carol Ember) disputed this conclusion by pointing out that Lee's evidence was too limited. Surveying 181 hunter-gatherer societies, Ember showed that the animal protein captured by both hunting and fishing provided over half of the calories for foraging people in most of these societies. Then, in 2001, Lewis Binford's survey of over 339 foraging societies showed that while Ember was generally correct, she failed to see that the relative importance of animal and plant foods varied according to climate as indicated by the latitude of the location of a society. Foragers living at lower latitudes (0-30 degrees) can easily find edible plants, and here gathering provides more than half of the diet. But at higher latitudes (46-60 degrees), hunting and fishing provide over 90 percent of the diet. This is an example of how the universal human nature of foraging varies in response to variable ecological circumstances. To understand this, we need a human behavioral ecology that explains how variable human behaviors are adaptive responses to particular social and environmental contexts.

Lee's claim that foragers are completely egalitarian has also been disputed. As I have indicated in previous posts (here), foraging societies do recognize informal leaders, although these leaders are checked by resistance to any arrogant dominance. Moreover, male hunters are unequal in their hunting skills. As Michael Gurven and Kim Hill (2009) have shown, hunting is such a difficult skill that some men never become successful hunters, and those men who are successful hunters have greater reproductive success, because women prefer skilled hunters, and men trade meat for sex. This suggests that Rousseau and Marx were wrong to assume that the state of nature was a state of complete equality.

As I have indicated in a previous post (here), anthropologist Marshall Sahlins tried in the 1960s to defend Rousseau's account of the state of nature by arguing that foragers lived in the "original affluent society." Like Rousseau, Sahlins claimed that although foragers were not affluent in the sense of being wealthy, they were affluent in the sense that their wants were so limited that they were easily satisfied with little effort, and therefore they were happier than people in wealthy societies whose artificial wants always exceeded their powers for satisfying them. Sahlins saw evidence that foragers had to work only a few hours a week to provide for all their subsistence needs, far less than the forty hours of work for typical workers in the industrialized societies. So it seemed that the foraging life was one of extensive leisure and little work. Anthropologists like Lee seemed to confirm Sahlins in pointing out that foragers like the !Kung in Southern Africa could easily feed themselves with Mongongo nuts and other edible plants that were abundantly available without any work required.

Although this foraging affluence thesis was accepted by many anthropologists, those who studied foraging societies had to admit that this idea was not well supported by the evidence. As surveyed by David Kaplan (2000) and Robert Kelly (2013), the evidence shows that foragers have to work long and hard to secure their subsistence, and that they often live on the edge of starvation. Sahlins and Lee had counted the hours devoted to foraging, but not the hours necessary for preparing and cooking food, for making and maintaining tools, and for building new huts when they move. All of these activities require far more than forty hours a week. And what Sahlins and Lee identify as hours of leisure are often hours of imposed idleness, as for example when !Kung must stay out of the midday heat of the African desert to avoid sunstroke and dehydration. Foragers like the !Kung show high rates of infant and child mortality, short average life spans, and stunted growth from insufficient diets. This hardly looks like affluence.

In overlooking this evidence of misery among foragers, and insisting that the foraging life is the happiest life for human beings, Sahlins and Lee were showing the bias of social scientists in the 1960s who wanted to criticize modern capitalist society by making the Rousseauian argument that the materialist consumerism, competitiveness, and inequality of capitalist life was depriving people of the happiness that their foraging ancestors had enjoyed. Lee made this clear when he observed that anthropologists studying foraging societies are looking for alternatives to the "poverty, injustice, exploitation, war, and suffering" of human beings in the modern world:

"When anthropologists look at hunter-gatherers, they are seeking something else: a vision of human life and human possibilities without the pomp and glory, but also without the misery and inequity of state and class society. . . . I am convinced that hunter-gatherer studies, far from being the fantasy of uncritical romantics, have a role to play . . . as part of a larger movement to recapture wholeness from an increasingly fragmented and alienating modernity" (Lee 1992, p. 43).

The main Rousseauian idea for Sahlins and Lee is that while foragers don't have much, they don't want much, and they can easily satisfy their limited wants, while people in modern bourgeois societies have unlimited wants that they cannot ever satisfy, and thus they are miserable. There is some evidence against this idea that foragers have limited wants, because anthropologists have noticed that foragers are often eager to have the goods that come from agrarian and Western societies: steel tools, shotguns and rifles, aluminum pots and pans, clothing from textile plants, motor boats, and all the conveniences of industrialized economies. I have written about this in a previous post (here).

Sanderson refers to this in concluding: "Virtually all nonindustrial populations have a great interest in modern technology" (49).He seems to contradict this conclusion, however, when he says that foragers often prefer to live as foragers because it's an easier life, and "people have no inherent desire to advance their level of technology" (52, 58).

In any case, there is evidence that foragers understand how to plant and cultivate plants. After all, some foragers are horticulturalists who tend gardens to supplement the food coming from hunting, fishing, and gathering. So why did agricultural societies not begin to appear until about 11,000 to 5,000 years ago? Part of the answer, Sanderson indicates, is that world climates were generally too cold, too dry, and too unstable prior to 11,500 years ago to make agriculture possible. But while the climate change to a warmer, wetter, and more stable climate enabled agriculture, Sanderson suggests, population pressure caused it, because increasing populations would have forced people into cultivating crops to produce enough food to feed themselves.

Since about 3,700 years ago, some groups have relied on herding animals with little or no agriculture. These pastoral societies have been common in parts of the world where there is too little water or warm weather to sustain agriculture--areas such as sub-Saharan Africa, the Arabian deserts, Central Eurasia, the Asian steppe, and Tibet.

Finally, the fourth fundamental way of organizing society for making a living--the modern commercial society--has become prominent only in the last 400 or 500 years and most prominent only in the last 200 years. The fact that capitalism has apparently arisen only very recently in human social evolution might suggest that it's a purely cultural invention with no roots in human nature. And, indeed, even proponents of the modern liberal social order like Friedrich Hayek have argued that market societies are contrary to the human nature that evolved in ancient foraging societies, and that the popular appeal of socialism can be explained as an atavistic yearning to return to the small foraging bands in which our prehistoric ancestors evolved. Evolutionary psychologists like Leda Cosmides and John Tooby have embraced this idea in claiming that there is a "mismatch" between the human nature shaped by the Pleistocene environment of evolutionary adaptation and the human culture of modern commercial societies.

In various posts (here), I have argued against this. Sanderson seems to agree with me. Although he concedes that the "mismatch" theory is at least partially true, because some innate propensities that were adaptive in the ancient past might not be adaptive today, he is skeptical about whether it is totally true (7-8, 126, 143). In particular, he suggests that capitalist social orders might satisfy the naturally evolved propensities for reciprocal exchange; and he cites Cosmides and Tooby as supporting this in a way that suggests that even they see capitalist social orders as satisfying some evolved propensities of human nature.

Adam Smith saw the opulence that results from exchange and specialization (the division of labor) as "the necessary, though very slow and gradual consequence of a certain propensity in human nature, which has in view no such extensive utility; the propensity to truck, barter, and exchange one thing for another."

Since capitalism has arisen so recently in human history and in such special circumstances. it might seem implausible for Smith to suggest that it is rooted in the innate propensities of human nature. But Sanderson suggests that we should understand this to mean that "capitalist relations lie dormant in human nature and develop when the preconditions appear" (68). The propensity to reciprocal exchange--the natural human tendency to truck, barter, and exchange--has been manifest throughout all of human history. There is some archaeological evidence for trading among ancient foragers hundreds of thousands of years ago. Large trade networks began to appear thousands of years ago. More recently, global trade networks have appeared with world commercialization.

To explain the evolutionary roots of this psychology of exchange, Sanderson quotes from Cosmides and Tooby's famous paper on "Cognitive Adaptations for Social Exchange," in which they presented their experimental studies of detecting cheaters (individuals who take a benefit without paying the cost) in Wason selection tasks. They saw this as an adaptive psychology for social exchange that evolved among our ancient forager ancestors. They thought this could be seen in studies of hunter-gatherer exchange:

"Despite the common characterization of hunter-gatherer life as an orgy of indiscriminate egalitarian cooperation and sharing--a kind of retro-utopia--the archaeological and ethnographic record shows that hunter-gatherers engaged in a number of different forms of social exchange (for an excellent review of hunter-gatherer economics, see Cashdan, 1989). Communal sharing does not exhaust the full range of exchange in such societies. Hunter-gatherers also engage in explicit contingent exchange--Fiske's 'market pricing'--in which tools and other durable goods are traded between bands, often in networks that extend over vast areas. A common form of trade is formal gift exchanges with carefully chosen partners from other bands. For instance, aboriginal Australians traded tools such as sting ray spears and stone axes through gift exchanges with partners from neighboring bands. These partnerships were linked in a chain that extended 620 km, from the coast, where sting ray spears were produced, to the interior, where there were quarries where the stone axes could be produced. Here, environmental variation in the source of raw materials for tool making allowed gains from trade based on economic specialization, and the laws of supply and demand seemed to operate. At the coast, where sting ray spears were common, it took more of them to buy an ax than in the interior, where spears were dear and axes cheap (Sharp, 1952). Similarly, the !Kung of the Kalahari desert range engage in a system of delayed reciprocal gift giving called 'hxaro' (Weissner, 1982; Cashdan, 1989), through which they trade durable goods such as blankets and necklaces" (Cosmides and Tooby, 1992, pp. 216-17).

Here, then, Cosmides and Tooby seem to disagree with Hayek's claim that the modern extended order of liberal societies organized through trade requires a repression of the natural human psychology shaped by the evolution of social life in ancient foraging bands. On the contrary, the modern liberal order can be seen as an expression of the evolved propensity for reciprocal exchange in modern conditions that allow for the extension of that propensity to embrace ever expanding social networks of trade. This conclusion is reinforced by evidence of neuroendocrine mechanisms (such as oxytocin) that foster the trust that facilitate social exchange. (A post on this can be found here.)

A post on various explanations for the Industrial Revolution--including Deirdre McCloskey's appeal to the rhetoric of the "bourgeois virtues"--can be found here.

Tuesday, April 19, 2016

To the question of the meaning and purpose of human life, the best answer--the answer we all give by the way we live our lives--is that we find the meaning and purpose of our lives in striving for the fullest satisfaction of our natural desires. Evolutionary science helps to explain why we are moved by the twenty natural desires of our evolved human nature. That scientific explanation is supported by lots of evidence. One of the best general surveys of that evidence is Stephen Sanderson's Human Nature and the Evolution of Society (Westview Press, 2014).

Some of what Sanderson says, however, seems to deny that science can teach us anything about the meaning and purpose of life. First of all, he warns against the naturalistic fallacy in inferring anything about moral values from natural facts. And, secondly, he dismisses teleological thinking about the ultimate purpose of life as mistaken. But implicit in Sanderson's writing is the recognition that we can rightly infer moral values from functional facts, and that even if we cannot find any cosmic purpose for life, we can find the immanent purpose of life inherent in our natural human desires.

After explaining the naturally evolved differences in the propensities and abilities of men and women, so that men on average are less inclined than are women to certain kinds of activities, Sanderson warns against the assumption that such natural tendencies tell us anything about what men and women should do. This is the naturalistic fallacy: deriving an "ought" from and "is." One cannot infer a moral judgment from a purely descriptive statement about how human beings behave. If men are naturally inclined towards careers such as firefighting, and women are naturally inclined towards careers such as nursing, it does not follow logically that men should be firefighters, or that women should be nurses (238).

And yet Sanderson seems to contradict himself in his writing about scientific research when he uses value-laden language--such as judging some behavior as "dysfunctional"--which seems to commit the naturalistic fallacy. For example, when he reports Harry Harlow's famous experiments with young monkeys reared by artificial mothers made of wire rather than real mothers. The monkeys exposed only to artificial mothers showed "severe emotional disturbance" and "dysfunctional" behavior, comparable to what happens to human children reared in orphanages without any maternal care (192-95, 210).

More generally, Sanderson concludes his book by arguing that evolutionary science can give an answer to the question of the meaning of life. "The meaning of human existence is to achieve satisfaction with respect to the basic goals and desires that are part of human nature. Since in real life these goals and desires are often in conflict, they must be harmonized or balanced in some way" (382). He then offers a slightly modified version of my list of twenty natural desires.

And while Sanderson rejects any teleological belief in "some deep cosmic purpose embedded in the universe or, more likely, in the mind of God," he does see a purpose embedded in the desires of human nature: "If there is no ultimate purpose to our lives, life is emptied of all meaning. Why then bother to live at all? The reason to bother is to fulfill the desires that emanate from our species-specific human nature. This is sufficient. There doesn't need to be anything else for life to be meaningful" (383, 386).

I agree. Even if science cannot support a cosmic teleology of purposes set by a Cosmic God, Cosmic Nature, or Cosmic Reason, science can support an immanent teleology of purposes set by human nature, human culture, and human individuals, by which human nature and human culture constrain but do not determine the purposes set by human individuals in deciding how best to rank and harmonize their natural desires over a whole life well lived.

And so, for example, we can judge that children deprived of parental care are likely to show "dysfunctional" behavior because it is hard for children to become happy adults if their natural need for parental care has not been satisfied.

In this way, a natural science of human nature can support moral judgments through the hypothetical imperatives of given-if-then reasoning: given the evolved human nature of our desires, if we want to live desirable lives, then we must live in ways that are most likely to satisfy those desires.

Tuesday, April 12, 2016

If the good is the desirable, then human ethics is natural insofar as it satisfies natural human desires that naturally win social approval as useful or agreeable to oneself or to others. The satisfaction of these natural desires constitutes a natural standard for judging social practice as either fulfilling or frustrating human nature, although prudence is required in judging what is best for particular people in particular social circumstances.

By this standard, the modern bourgeois liberal regime can be recognized as the best regime so far in human history, because no other regime has satisfied those natural desires so well for so many people. Or, to put it another way, the liberal regime has been more successful than any other regime so far in securing for human beings their equal liberty for the pursuit of happiness.

I have argued that these twenty natural desires are universally found in all human societies, that they have evolved by natural selection over millions of years of human evolutionary history to become components of the species-specific nature of human beings, that they are rooted in the physiological mechanisms of the brain, that they direct and limit the social variability of human beings as adapted to diverse ecological circumstances, and that different individuals with different temperaments will rank these desires differently.

My selection of these twenty desires as natural and universal is supported by various kinds of evidence. Social scientists who have surveyed the anthropological evidence have shown that there are hundreds of human universals, which are clustered around the twenty desires on my list. Psychologists who study human motivation recognize these twenty desires as manifesting the basic motives for human action. Survey data from psychologists who ask people what is most important to them confirm the primacy of these twenty desires. When Aristotle, in the Nicomachean Ethics and the Rhetoric, reviews the common opinions of human beings about what is desirable in life, he includes the twenty desires on my list. When an Aristotelian scholar like Martha Nussbaum describes the "basic human functions" that support universal norms of moral judgment, she includes the desires on my list.

There is evidence that this pattern of twenty desires developed in the Pleistocene environment of our hunting-gathering ancestors, from about 1.6 million years ago up to the invention of agriculture about 11,000 years ago. This was the evolutionary environment in which human nature was shaped by natural selection. The historical record of human civilization since the development of agriculture shows human beings as moved by these twenty desires.

My survey of the evidence is not as good as that provided by Stephen Sanderson in two of his books--The Evolution of Human Sociality (Rowman and Littlefield, 2001) and Human Nature and the Evolution of Society (Westview Press, 2014). Sanderson is one of the few sociologists who has promoted a Darwinian science of sociology. Of all the social sciences, sociology has been most resistant to Darwinian science, because so many sociologists believe that human society is a purely cultural construction unconstrained by human nature. Like me, Sanderson argues that while society certainly is "socially constructed," these social constructions are not arbitrary products of an autonomous culture. Social constructions are constrained by the natural desires and natural conditions of human existence. Human biological nature constrains but does not determine human cultural history and the choices of human individuals. Consequently, a Darwinian social science must explain the universality of human natural desires and the variability that comes from variable socioecological conditions and variable temperaments of individuals. Sanderson shows how that can be done.

Comparing the lists, one can see that he has made some changes. He has moved "health" from number 11 on my list to number 2. He has changed "justice as reciprocity" to "reciprocal exchange." He has added "ethnic identity" to the list. And he has omitted from his list seven of the desires on my list: (6) friendship, (10) war, (14) speech, (15) practical habituation, (16) practical reasoning, (17) practical arts, and (20) intellectual understanding.

I do not see the justification for omitting these seven, especially since all of these seven desires appear in one way or another in his writing. He says that friendship could rightly be added to his list (2014, pp. 12, 383). He writes about the evolution of war (2001, pp. 318-330; 2014, pp. 287-312) and of language (2014, pp. 27-32). He suggests that intellectual understanding should be added to his list (2014, p. 383).

Sanderson agrees with me that the natural desires cannot all be satisfied at the same time, or even over a whole life. And so people must rank these desires, and since individuals differ in their natural temperaments and abilities, they will differ in how they rank these desires. So, for example, as Sanderson observes, Albert Einstein said that he had no need for money, power, or fame to be happy; and so he was not much moved by the natural desires for social ranking, wealth, or political rule. Einstein said all he needed were his sailboat, his violin, and physics. And since he spent most of his time on physics, he was clearly ranking his natural desire for intellectual understanding over the other desires (2014, p. 383). For me, this shows the need for practical habituation and practical reasoning in organizing a life for the fullest and most coherent satisfaction of one's desires over a whole life.

Tuesday, April 05, 2016

Leo Strauss taught his students at the University of Chicago that any serious student of the history of political philosophy must assume the possibility that what the great philosophers have taught might be true. Writers of the textbooks on the history of political philosophy--like that of George Sabine--had assumed the truth of "historicism"--that all the great philosophers have been so imprisoned by the cultural prejudices of their time and place that they could not see the truths about political life that contemporary readers can see today. But Strauss argued that historicism is itself the great cultural prejudice of our time that cannot be affirmed as true without contradicting itself, and therefore serious thinkers must consider the possibility that the human mind can free itself of common opinions and apprehend what is simply true, and thus that the great philosophers--from Plato and Aristotle to Rousseau and Nietzsche--might help us to see some truths about human nature and human history that go beyond the largely unexamined opinions of our day.

Roger Masters was one of the students at Chicago who was persuaded by Strauss's argument, and Masters devoted himself to the careful study and translation of the writings of Jean-Jacques Rousseau, with the thought that Rousseau was one of those great philosophers who might teach something about the truth of human nature and politics. Masters became one of the leading translators and scholars of Rousseau in the 1960s. He was particularly interested in Rousseau's account of the state of nature and social contract reasoning as compared with Thomas Hobbes and John Locke.

Then, in the 1970s and 1980s, Masters began to study evolutionary science and Darwinian anthropology, with the thought that this science of human evolution might illuminate the debate between Hobbes, Locke, and Rousseau over the state of nature. Masters thus became one of the first political scientists to apply Darwinian science to the study of political philosophy.

According to Rousseau, neither Hobbes nor Locke recognized that in the state of nature human beings were so completely solitary that they would have lived in a state of peace and equality without any dependence on other human beings. Masters wrote this as his English translation of one of Rousseau's passages in the Discourse on the Origin of Inequality:

"Alone, idle, and always near danger, savage man must like to sleep, and be a light sleeper like animals which, thinking little, sleep so to speak all the time they do not think. His self-preservation being almost his only care, his best-trained faculties must be those having as principal object attack and defense, either to subjugate his prey or to save himself from being the prey of another animal." (Rousseau 1964, 112)

This was published in 1964 in Masters' edition of The First and Second Discourses.Then, in 1982, when Masters read Frans de Waal's Chimpanzee Politics, which describes the complex political lives of chimpanzees competing for power and alpha male dominance in small groups, Masters saw that this implied that the earliest evolutionary ancestors shared with chimpanzees and human beings were probably highly political animals. He also saw that anthropologists studying the societies of human hunter-gatherers had shown the complex social order of these primitive human groups. Consequently, it seemed that biologists and anthropologists had shown that human beings in a state of nature could not have been utterly solitary, as Rousseau claimed.

And if Strauss was right about taking seriously the possibility that the teaching of a great philosopher like Rousseau could be true, this must include the possibility that the teaching could be false. Philosophers make empirical claims about human nature and human history that could be either confirmed or denied by scientific research. So, Masters had to admit that Rousseau's teaching about the state of nature had been refuted by Darwinian science. "Like chimps," Masters concluded, "humans are by nature social animals with innate political behaviors of a sort ignored by Rousseau in the passage I'd translated" (Masters 2013, 227).

I agree with Masters about this, because in a series of posts, I have argued that the evidence from evolutionary science and political anthropology allows us to judge the philosophic debate over the state of nature and to conclude that while Rousseau was mostly wrong, Hobbes was partly right, and Locke was mostly right. This illustrates how the study of the history of political philosophy can become a biopolitical science.

Consider, for example, how Locke's account of the human family as the "first society" in the state of nature is confirmed by the "embodied capital theory" of the evolution of human life history, which is supported by lots of evidence gathered by Darwinian primatologists and anthropologists.

In the Two Treatises, Locke gives both religious and natural explanations for human familial bonding in the state of nature. It shows the "wisdom of the great Creator" that He has created human beings with desires for monogamous marrying and for mothers and fathers jointly caring for their children (1970a, 86-89; 1970b, 77-80). This can also be explained through the natural history of animal reproduction as adapted to the feeding niche for each species. For some frugivorous animals who feed on grass and plants, whose offspring can survive shortly after birth without much parental care, Locke explains, mothers care for the offspring with no need for fathers to provide any parental care, and consequently there is no need for any enduring bond between the sexual mates. But for those carnivorous animals who feed on meat from hunting, there is a natural need for an enduring pair-bonding of the sexual mates to provide biparental care. If mothers cannot feed themselves and their offspring without the help of males, because they need the meat provided by male hunting, or if birth-spacing is short that mothers can often have multiple dependent offspring requiring prolonged care from both parents, then these animals will have a more enduring conjugal bond; and this is true for human beings. As compared with other animals, human offspring are dependent on adult care for a long period of childhood, in which children cannot produce enough food to feed themselves. During this period of dependence, offspring must be not only nourished but also educated, because complex human social life requires a prolonged period of social learning in which children learn the skills they will need to become productive adults.

In contrast to Locke, Rousseau argued that human beings in the "pure state of nature" were asocial and almost completely solitary animals. Men and women encountered one another by accident and engaged in sexual intercourse whenever the desire moved them, and then they immediately left each other and felt no tie to one another. Mothers nursed their children for a short time. But as soon as the children could feed themselves, they left their mother, and they soon would no longer recognize one another. So while the maternal attachment to children was the one social bond in the state of nature, it was only a momentary bond that created no enduring social recognition between parents and children and no support for the mother and child from the father (Rousseau 1964, 108, 112, 120-21, 130-31, 137, 142, 147, 216, 219).

In one of the longest notes in the Second Discourse (1964, 213-20)--note l--Rousseau quotes the entirety of sections 79-80 of Locke's Second Treatise, where Locke lays out his reasoning for monogamous pair-bonding and biparental care in the state of nature. Rousseau denies the factual truth of Locke's claims about animal reproduction and parental care, and accuses him of making the same mistake that Hobbes made in projecting what we see in human beings today back into the state of nature.

Against Locke, Rousseau insists that primitive human beings were totally frugivorous in their feeding and not at all carnivorous. Mothers and children who feed on grass and plants can easily feed themselves without any need for meat from male hunters. Furthermore, Rousseau argues that fact that human females have only two teats indicates that they rarely have more than one child at a time that needs care, and thus mothers and children have no need for help from the men.

Over the past 100 years, studies of human hunting-gathering societies and comparative studies of other primate and mammalian societies have provided evidence that Rousseau was mostly wrong, and Locke was mostly right. This evidence shows that as compared with other mammals and primates, human beings show at least five distinctive traits (Balshine 2012). The first four pertain to human life history. Human beings have an unusually long lifespan. They have also have an unusually long period of juvenile dependence on adults. They show an unusual pattern of support for reproduction from older post-reproductive adults. And they show male support of reproduction through the provisioning of females and their offspring. The fifth distinctively human trait is unusually large brains that bring increased capacities for social learning, teaching, and thinking about cognitively challenging problems. Human hunter-gatherers, who live in what the early modern philosophers called the state of nature, show all of these traits.

One persuasive evolutionary theory that fits all of this evidence for these distinctively human traits is the embodied capital theory developed by Hillard Kaplan and his colleagues (Kaplan et al. 2000). The main idea is that the human species show an evolutionary adaptation for a feeding niche based on high-quality, nutrient-dense, and difficult-to-acquire foods, which is a skill-intensive niche that requires extended learning through big brains.

Chimpanzees and other nonhuman primates feed mostly on leaves, small, unripe fruit, and large, ripe fruit, which constitutes over 90% of their diet. Gathering this food requires so little skill and effort that young chimpanzees after they have been weaned can gather enough to feed themselves. Chimpanzees do extract some food from nuts and insects in ways that require some skill that has to be learned. And the males do engage in some hunting that requires some skill. But the extracted food and the hunted meat is a very small portion of their diet, and the skills required for acquiring this food are not very complicated.

By contrast with chimpanzees, over 75% of the diet of human foragers is meat from hunting, which requires great skill that comes only from adult males who have learned those skills over a period of 30 years or more. In contrast to leaves and fruit, meat is higher quality food, rich in protein, and highly concentrated, but it is also more difficult to acquire. Hunted meat provides the nutrition necessary for the growth and maintenance of big brains that consume high levels of metabolic energy. And it is these big brains that are necessary for learning the skills necessary for successful hunting.

Unlike chimpanzees, adult male human foragers must produce food for the feeding of women and children. Human children consume more food than they produce until about age 20. Human females consume more food than they produce throughout their childhood and their years of reproductive fertility. Human females produce slightly more than they consume only after menopause and before old age. Human females can have shorter birth intervals than apes do, because human females get food subsidies from adult male hunters, so that mothers can care for two or more children at a time. Most of the production of food comes from adult males (ages 25-55) through hunting, who share their food with women and children.

Tracking and killing wild game of many different species is an intellectually challenging problem that takes many years of social learning with a large brain that requires many years of growth. Consequently, both mothers and fathers must make many years of resource investments in the rearing and educating of their children before they can become productive contributors to reproductive fitness.

If this is the scientific description of the state of nature--of the original life of our earliest human ancestors--then Locke was mostly right, and Rousseau was mostly wrong. This would then be an example of how Darwinian science can contribute to the study of the history of political philosophy by helping us to judge the claims that the philosophers have made as being true or false.